Currently less than .4% of the slaughtered pigs contain sulfamethazine at levels above those allowed by the Food and Drug Administration. These violations are due partly to failure to properly withdraw sulfamethazine after treatment to reduce loss or combat or prevent diseases, whereas others are due to inadvertent contamination of feed or the environment. Cull animals particularly are suspect. The National Pork Producers Council (NPPC), representing more than 100,000 producers, is supporting attempts to reduce violations and maintain the safe image of pork. The Food and Drug Administration is continuing to evaluate the safety of sulfamethazine, and the NPPC has encouraged producers to suspend use of the drug. The NPPC is encouraging development of faster, more reliable testing methods and of a traceback system to permit the farm of origin to be identified. But the NPPC is opposed to the "bill back" proposal developed by the Packers and Stockyard Administration that would allow packers to charge the seller for costs of carcasses condemned for containing illegal residues. Reasons for opposition include imprecision of current testing procedures, inaccuracy of present identification and traceback methods and disruption of the free market relationship between buyers and sellers.